Monday, 22 May 2017

I noticed a few weeks ago that the SQ4 was trying to drive into the kerb, and required constant correction to keep it on track. There are some roads with steep camber around here which adds to the effect, but on some fast, flat A-roads it still happens, so I need to look at wheel alignment.

To do this, you need to set up a straight edge along the length of the bike to provide a datum for the wheels. Since I don't possess a laser and most of the timber I have is anything but straight, a piece of string is the best solution.

Tie a length of string to a spoke at the front of the front wheel and wrap is around the tire, running the string to the back.

Pull the string tight - you can wrap the string around the back of the rear wheel and tie it off on something convenient. It's very useful to have a bike with a rear stand here, because centre stands get in the way of your string.

You'll note the chopstick under the string at the front. This is there because I have a 3.50 - 19 tyre at the front and a 4.00 - 19 tyre at the rear - so the diameter difference is 0.5" and I have provided a 1/4" spacer (the chopstick) to compensate for this difference.

There is a 1/4" gap at the rear of the front tyre, due to the diameter difference to the rear tyre.

Unfortunately, I also have a gap between the string and the front half of the rear tyre. This is because the rear wheel is not aligned with the front wheel.

You can see this gap here:

Use the tool kit spanners to slacken the wheel spindle:

Use the chain adjusters to move the spindle forwards or backwards. Since my chain tension is correct, I don't want to move the nearside of the rear wheel - I will correct the alignment by pushing the offside forwards.

Now, the front and rear edges of the rear tyre touch the string. I'll check the front wheel has not moved and the string is straight:

Tighten up the wheel spindles and the lock nuts on the chain adjusters and you are done.

As you all know, the W/NG has not been in my hands for long. As we know little of its past, we need to do a oil & filter change, 1940's style.

First off, we need to remove the sump plate to drain the crankcase and get some access to the sump strainer:

It's normally held in place with four 1/4" BSW hex screws, wired in place. No wire here! Removing the screws, I'm a little concerned that two come out with the proper 1/4" BSW spanner, and two come out with a 10 mm spanner.

I shouldn't have been concerned though, I have seen imperial fasteners with heads filed to fit metric spanners before on this bike, and these are no exception - all 1/4" BSW:

The strainer looks good too. We'll clean that before it goes back:

It looks like the scavenge pump is working, as there is nothing in the sump:

I'm going to leave the oil draining for a while and I want to make sure the whole system is drained, so I have disconnected the two oil lines at the timing chest:

I noticed a while back that the magneto platform flexes more than it should, and this became more apparent when I set the ignition timing recently. It's down to the fact that the bolt retaining the magneto platform to the timing cover is missing, and the reason it is missing is that the boss it screws into is also missing...

Removing the magneto chain cover revealed another problem - a missing screw, replaced with a countersunk brass screw of dubious provenance, and within the cover, a burst screw boss:

So we need a man who can TIG weld aluminium and who has experience repairing old castings...

Here's the timing case, removed and cleaned:

This is the damage to the magneto platform bolt hole:

It went to Roo at Roadkill Customs in Cromer to be fixed. He TIG welded the holes up:

I've used a stud, rather than the original screw. The original is tapped 5/16" CEI into the alloy, with a hex screw - heaven knows why it was specified like that.

This is a 5/16" CEI x 5/16" BSW stud. At 1 1/8" its a bit long, but can easily be shortened if need be, and the BSW thread will be stronger in the alloy.

I also replaced the rocker oil feed union while I had the timing case off. The thread was a bit mangled; a self grip wrench and a blowlamp were needed to get the old one out.

Draganfly have stock of these - I put this in and tightened it with the aid of a 1/16" twist drill:

I'm using some Threebond 1215 silicone gasket to replace the timing cover. It's grey, discrete and rated at 250°C. Ample for this application.

We need the additional paper washer over the oil pump pickup pipe:

New gasket, applied over a thin bead of Threebond:

And the timing case in place. The magneto pinion is held in place with a Velcro tape, awaiting arrival of the magneto. The breather has been annealed and straightened and the magneto platform is now retained to the new stud with a 5/16" CEI nut and a shakeproof washer.

Thursday, 4 May 2017

Monday, 1 May 2017

While putting the kickstart & gear selector case together after the spring incident, I noticed that the selector pawl persistently fell off as I replaced the outer case. With the SQ4, I don't remember having a problem reassembling this complex bit of the gearbox.

Something was wrong.

Pulling the selector apart, I realised that the pin on which the pawl pivots was loose, and that the small springs were not moving freely. Investigation found the pin bursting out of the spring box casting:

In the absence of a better solution, I fixed the pin with Araldite Steel and scraped the spring box enough for the small springs to move freely. At the same time, I searched eBay and put an advertisement on the AOMCC forum:

I never tested the repaired spring box, though I am sure it would have worked (but not for how long). I now have this fine replacement, very kindly provided by Guy Hovey after a plea on the AOMCC forum:

So this is now in place, the box back together and selecting gears again.

The way this works is interesting.

Movement of the gear lever is transferred into the interior of the box, moving a short internal lever (item 37 in the picture below), which has a pin fixed at one end

The pin moves up or down against the small springs, moving the pawl (item 36) about its pivot until they become coil bound. The pawl is now engaged with the selector quadrant.

More gear lever movement then moves the whole spring box against the large springs, which are resisted by the pin screwed into the outer case, behind the gear lever.

The pawl moves the selector quadrant (item 35), changing gear

When pressure on the gear lever is released, the pawl moves back over the teeth cut in the quadrant and returns to the central relaxed position.

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About Me

I'm a mechanical engineer by profession, working these last 25 years in the oil & gas industry. I've been riding bikes since I was 16, and spend my time tinkering with classic cars & bikes when I'm not working or looking after the house.
I'm married & have two great kids, who mostly share the passion!